Dehydration of air or the like and gaseous mixtures



Nw, 29, 1932. R. w. THOMAS ET A1.

DEHYDATION OF AIR OR THE LIKE AND GASEOUS MIXTURES Filed May 1l. 1929 YKMNEOnS Q m s@ T www A\OM mmwz 1oxm kmr G. @heffezz Syvum/Wow .W Thomas,

atto/mam Patented Nov. 29, 1932 UNITED STATES PATENT OFFICE ROSSWELL W.THOMAS AND GEORGE G. OBERFELL, OF BARTLESVILLE, OKLAHOMA,

ASSIGNORS TO PHILLIPS PETROLEUM COMPANY, OF BARTLESVILLE, OKLAHOMA.

DEHYDRATION OF AIR OR THE LIKE AND GASEOUS MIXTURES Application filedMay 11,

This invention relates generically to the dehydration of gases such asair, and speciiically to the dehydration of air to be used in an air andgas mixture, by heat exchange with the gas employed in the mixture.

In the manufacture of an air-gas mixture for domestic or industrialconsumption, it has heretofore been the practice to use mechanical orindirect heat orjrefrigeration for the dehydration of air used in themixture. T he need for dehydration is evident when the temperature ofthe air entering the pipe lines is substantially different from thetemperature of the pipe line itself, or the surroundings. A suddenchange in temperature causes a condensation which is distinctly harmfulto the use of the mixture. For instance, if the air is not dehydrated,and it carries'a sub.

stantial percentage of moisture, this moisture,

on condensing, is not alone liable to clog the pipe lines, but mayfreeze and cause rupturing of the lines. Furthermore, when the air isnot dehydrated, it necessitates drips and the cost of pumping the drips.By the present invention, all the drips and the cost of pumping the samewill be eliminated.A

The present process differs from the ones heretofore known, in that thelatent heat of vaporization of the liquefied hydrocarbon gas to be usedin the mixture, is used in heat exchange relation with the air todehydrate the latter before the air enters the mixture. One of theadvantages of such a system resides in the fact that the heat exchangerelation of the hydrocarbon gas and the air in the dehydration process,provides for some of the heat of vaporization necessary in thevaporization of the fuel.

From the foregoing, it will be manifest that the primary object of theinvention is to provide a novel system in Awhich the hydrocarbon gas tobe used in an air-gas mixture is employed in dehydrating the air used insuch mixture.

With the foregoing objects outlined and with other objects in view whichwill appear as the description proceeds, the invention consists'in thenovel features hereinafter de- 50 scribed in detail, illustrated in theaccom- 1929. Serial No. 362,438.

panyinc` drawing, and more particularly pointed` out in the appendedclaims.

The drawing shows a diagrammatic view of one form o apparatus forpracticing the method.

It has heretofore been proposed to utilize light hydrocarbons boilingbelow 100 F. for the purpose of diluting the air forming an air-gasmixture. For example, one roposal includes the mixing of substantia yure butane with air, in the proportions of a out 15% butane vapor andabout 85% air by volume. In makingl such mixtures, it has been necessaryto de ydrate the air to eliminate the objections above mentioned. If thepresent invention is used in such a system, the light hydrocarbon orhydrocarbons such as ethane, propane, butane or mixtures of the same,may be stored in the tank, shown in the drawing. These hydrocarbons havevapor pressures of not less than 25 lbs. per square inch, and notgreater than 500 lbs. per square inch at ordinary temperatures. Fromthis tank, the gas maybe fed by way of a conduit 2, through a regulatinor expansion valve 3, and into a pipe 4. f course, a fuel such assubstantially pure butane, a liquid, if permitted to expand or vaporize,vv1ll-decrease in temperature, so in its cooled condition, the fuel isfed by the line 4, into a heat exchanger v5, where it travels around thetubes 6, and nally exits through a valved conduit 7 which introduces thesame into a vaporizer 8 of the tubular .ty e. This vaporizer is heatedby any suitab e agent, such as steam, hot water, etc., which entersthrough the pipe 9 and is discharged through the pipe 10. The fuelvaporized in the part 8, travels through a conduit 11, having a suitableregulating valve 12, and is discharged into a roportioning or mixingmechanism 13 w ere it is mixed in proper proportions wit air or thelike, and the air-gas mixture is discharged by way of a pipe 14, whichleads the same to storage or to a pipe line.

Valves 20 in the conduits 2, 4 and 7, permit the feeding of the lighthydrocarbon material directly to the vaporizer 8 when desired, withoutpassing the same through the heat exchanger 5.

The air or 'other suitable gas employed in the system enters the heatexchanger 5 at the point 15, and it, of course, may be forced in underpressure. This air travels through the tubes 6 inlheat exchange relationwith vthe fuel gas, and consequently, the temperatureof the air islowered so that substantially all the moisture is condensed out and maybe discharged by way of the line 16. By controlling the expansion valve3, greater or less expansion of the fuel gas may take place, in orderthat the temperature of the heat exchanger may be regulated.Furthermore, the air is not alone dehydrated in the heat exchanger 5,but it imparts its heat to the fuel gas, so that the latter is partiallyvaporized before entering the vaporizer 8, in which it is completelyvaporized.

A conduit 17 connects the heat exchanger 5 to the proportioningmechanism 13, and functions to feed the dehydrated air from the heatexchanger to the mechanism 13.

It is advisable in a system of this character to pipe the a'ir from theexterior of the building in which the machinery is housed. This addssomewhat to the safety of the plant, particularly in case any butanevapors or the like escape in the mixing machine room, and are drawn intothe air intake, and it is also of some virtue when it is desired topartially dehydrate the incoming air by means of chilling the same inthe heat exchanger with the boiling butane or the like, from which vaporfor the system is evolved.

In operating the system, the light hydrocarbon or hydrocarbons is firstexpanded into the air cooler or heat exchanger 5, and the air taken into the mixing machine 13 passes through the cooler prior to entering themixing machine. Due to the particular temperature level involved, only asmall part of the latent heat of vaporization will be transferred to theincoming air, and as a consequence, a mixture of hydrocarbon liquid andvapor will pass from the heat exchanger 5, into the second or mainvaporizer 8, in which the remainder of the latent heat of vaporizationwill besupplied by steam, hot water, etc.

The pressure regulator 3 on the liquid line 2, can be so adjusted thatthe temperature level in the air cooler will be such that the airpassing to the mixing machine 13, will be at 33 or34 F. This means thatany moisture condensed from the air can be drawn off from the lower endof the heat exchanger through the pipe 16, in a liquid condition,whereas if the temperature is held below the freezing point of water,such condensate would freeze on the tubes, and eventually l, stop upthe. apparatus entirely. It is probably best that this preliminaryvaporizer 5 should be laid horizontally with the air passing through thetubes 6, and the boiling hydrocarbon or' hydrocarbons surrounding and z:submerging all of the tubes and occupying the shell space. Acounter-curnent iiow between the air and the fuel gas can be arranged.However, this would be of no great advantage, as all of the tube surfacewould be subjected to about the same temperature. As stated above, themixed liquid and vapor 'would pass then into the bottom of the verticalvaporizer. 8, and the process would con- Atinue in the normal manner.

vmight be high as would be the case during or just after a summershower, a very considerable amount of water would be condensed.

Some of our preliminary calculations are shown below for illustration.

1 M cu. ft. 540 B. t. u. butane-air mixture has 169 cu. ft. butane vaporof 1.95 Sp. Gr.

1.95 Sp. Gr.X.077 lbs. per cu. ft. (air) 169 cu. ft.=25.3 lbs. butanevapor per M cu. ft.

831 cu. ft. of air per M finished gas .047 lbs. per cu. ft. at F.=39lbs. air per M cu. ft. .237 specific heat of air=9.23 B. t. u. per F.change in air temperature.

25.3 lbs. butane per MX 170 B. t. u. per lb. latent heat ofvaporization=4301 B. t. u. refrigeration per M cu. ft. finished gas.9.23 B. t. u. per F. dropped in air temperature= 467 F. possibledecrease in air temperature.

It is known that this decrease is impossible due to the temperaturelevel at which the butane will take on this latent heat of vaporization,however, it is very easy to reduce the air temperature to 33 or 35 F.with only a small amount of exchange surface. The value of K should befairly high due to the boiling liquid on one side of the tubes, althoughthe low velocity air stream on the other side will tend to hold thisvalue down Assuming a regular summer time condition with the intake airat 90 F. and a relative humidity of we note that the vapor volumecontent of water in air is .047 at F. which, when multiplied by .70relative humidity, equals .0329 parts H2O in the air under theseconditions. If this4 air is cooled to 40 F., the water-vapor contentwill be .0082 parts by vapor volume, therefore, under practically anysummer time condition, this dehydration will be very effective and evennecessary to prevent condensation in the pipe line.

The Idew point of the water vapor in the air will be still furtherdecreased by the admixture of the 16.9% of butane vapor. 1n one example,which we worked out where the air had'been cooled to 40 F. and had aWater-vapor content of .00823 parts by vapor volume, the final resultsafter mixing with sucient butane to produce a 540 B. t. u.` gas (whichtook .831 parts of air and .169

parts of butane vapor), the final composition of the finished gas was.00683 parts H2O, .82417 parts air, .16900 parts butane, 1.00000 totalat 14.7 pounds absolute times .00683 parts H2O, We nd the absolutepressure effective on the Water vapor to be :1004 pounds and checkingback, We note that the dew point of the Water vapor has been lowered to35 F. or 5 due to the butane percentage therein.

The terms and expressions employe-d herein are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms, and expressions, of excluding any equivalents of thefeatures shown or described, or portions thereof, but it is recognizedthat various modifications' are possible Within the scope of theinvention claimed. f

What we claim and desire to secure by Letters Patent is:

1. In a method ofthe character described, vaporizing a liquefiednormally gaseous hydrocarbon material to absorb heat, passing aircontaining moisture in heat exchange re` lation with said material Whilethe latter is undergoing Taporization for the purpose of condensing themoisture out of the air, and subsequently mixing the dehydrated air andvaporized hydrocarbon material to produce a combustible mixture.

2. In a method of the character described,

the deh drated air with the vaporized fluid the flui forming not morethan 25% of sai mixture.

6. ln a method of the character described, vaporizing a liquefiednormally gaseous hy drocarbon material having a vapor pressure of notless than 25 lbs. persquare inch and not greater than 500lbs. per squareinch at ordinary temperatures, passing moist air in heat exchangerelation with said material while the latterv is undergoing vaporizationfor the purpose of condensin the moisture out of the air and heatingsaid gaseous hydrocarbon material, and subsequently mixing thedehydrated. air and vaporlzed hydrocarbon material to produce acombustible mixture.

GEORGE G. OBERFELL.

ROSSWELL W. THOMAS.

vaporizing a liquefied normally gaseous hydrocarbon fluid, passing moistair inA heat exchange relation with the fluid While the latter isundergoing vaporization, subsequent- Y ly heating said fluid tocompletelyvaporize the same, andA then mixing the vaporized fluid Withthe dehydrated air.

3. In a method of the character described storing a normally gaseoushydrocarbon fiuid in liquefied condition, feeding the liquefied fluidfrom storage While permitting the same to vaporize, passing the fluidWhile it is undcrgoing vaporization in heat exchange relation to moistair, and thereby condensing moisture out of the air and heating thefluid, and subsequently mixing the dehydrated air with the vaporizedfluid to produce a combustible mixture.

4. ln a method of the character described, vaporizing a normally gaseoushydrocarbon fluid from liquid to gaseous state, utilizing the reducedtemperature thus created to condense moisture out of air, and thenmixing the dehydrated air with the vaporized fluid.,

5. ln a method of the character described,

vaporizing a normally gaseous hydrocarbon fluid from liquid to gaseousstate, utilizing the reduced temperature thus created to condensemoisture out of air, and then mixing

